1. Field of the Invention
The present invention relates to a method and device for processing an image in which a portion corresponding to a subject is extracted from plural shot image.
2. Description of the Prior Art
In various fields such as a computer graphics, an industrial design, or making of 3-D web contents, a three-dimensional data input system is used for digitizing a solid shape of an object.
One of three-dimensional data input methods is called a shape-from-silhouette method. In this method, plural images obtained by shooting an object are used for extracting a shield contour (i.e., a silhouette) form each of the images, and a three-dimensional shape of the object is estimated from the extraction result and information of shooting positions. As an example of the application of the shape-from-silhouette method, Japanese patent publication No. 61-138377 discloses a technique for reconstructing a shape of an object by disposing a virtual object made of plural shape elements called voxels gathering in a three-dimensional virtual space, calculating a common portion of visual volumes determined by eye points of shooting and the shield contours, and connecting the voxels corresponding to the common portion.
Accuracy in reconstructing a shape of an object using the shape-from-silhouette method depends on how accurately the shield contours are extracted from each image. Under present circumstances, it is difficult to obtain a good result of extraction that can satisfy the demand of a user by completely automatic image processing, and an instruction or a correction is required to the user. Using a sophisticated image processing technique that utilizes knowledge of an object and a background, the accuracy of the extraction will be improved to some extent. However, it will require much time for inputting the knowledge, the object is limited, or the system is expensive. Moreover, even if a technique of extracting shield contours from shot images by disposing a screen of a uniform color as a background for color clustering, a partial error of extraction cannot be avoided since real background color is not uniform due to a shadow or unevenness of lighting.
On the other hand, in order to reproduce a shape of an object precisely and correctly by the shape-from-silhouette method, as many portions as possible of a surface of the object should appear as shield contours in the images. A surface having a large curvature should be shot from various positions. Therefore, the number of necessary images becomes extremely large for an object having a complicated relief.
Conventionally, there is a problem that a processing time necessary for extracting the shield contours increase proportionally to the number of images necessary for reconstructing the shape of the object, and that a burden of the user who corrects the result of the extraction increases.